New lung cell type identified.
There are two classifications of cells in the human body, namely, germ cells which are used to make sperm and eggs, and somatic cells that make up every other cell in the body including lung cells. The lung epithelium is composed of a variety of cellular lineages which reside in anatomically specific niches from the trachea to the conducting airways to the alveoli. Due to technological advances in genome-wide transcriptional profiling and single-cell sequencing studies have revealed a more complex population of lung epithelial cells. Now, a study from researchers at Boston University School of Medicine identifies a new lung cell type which is implicated in the body’s innate immune defense against the bacteria Streptococcus pneumoniae, one of the leading causes of pneumonia worldwide. The team state that their findings may lead to new, non-traditional approaches in the fight against pneumonia and chronic lung diseases. The opensource study is published in the Journal of Clinical Investigation.
Previous studies show that P-element–induced wimpy testes (Piwi) proteins and their name, is reflective of their functional role in the male germline. It was thought that the MIWI2 gene was only expressed in male germ cells as part of a family of genes which ensure the proper development of sperm. The current study shows that the same gene is expressed in somatic cells in the body, and marks a distinct population of previously unknown multiciliated cells which line the upper airways of the lung.
The current study identifies a subpopulation of multiciliated airway epithelial cells which express MIWI2. Results identify both the number of MIWI2-positive cells and the degree to which they express this factor increase during lung infection. Data findings via RNA sequencing demonstrated that MIWI2-positive cells have a significantly different transcriptome compared with neighbouring multiciliated cells which do not express MIWI2.
The lab state that MIWI2 loss-of-function studies revealed a functional role for MIWI2 in the homeostatic balance of ciliated and secretory cells in the conducting airways and in shaping innate immune responses. They go on to add that these results revealed that multiciliated cells, which have previously been thought to be homogenous, can be reclassified into MIWI2-positive and MIWI2-negative subsets; more broadly, they provide the first evidence that Piwi proteins are functional in noncancerous somatic tissue.
The team surmise their data identifies a previously unknown subset of airway multiciliated cells which can be discriminated by MIWI2 expression. They go on to add that what sets this new population of ciliated cells apart is that they express the MIWI2 protein and were found to have a specialized role in controlling lung infection. For the future, the researchers state the new cell type and pattern of gene expression may also lead to a better understanding of the mechanisms behind diseases like COPD and asthma, inflammatory conditions that involve changes in the airway cellular composition.